
11. EMERGENCY STOP SIGNAL
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11
EMERGENCY STOP SIGNAL
Using the emergency stop signal effectively enables the design of safe
machine tools.
The emergency stop signal is provided to bring a machine tool to an
emergency stop. It is input to the CNC controller, servo amplifier, and
spindle amplifier. An emergency stop signal is usually generated by
closing the B contact of a pushbutton switch.
When the emergency stop signal (*ESP) contact is closed, the CNC
controller enters the emergency stop released state, such that the servo and
spindle motors can be controlled and operated.
When the emergency stop signal (*ESP) contact opens, the CNC
controller is reset and enters the emergency stop state, and the servo and
spindle motors are decelerated to a stop.
Shutting off the servo amplifier power causes a dynamic brake to be
applied to the servo motor. Even when a dynamic brake is applied,
however, a servo motor attached to a vertical axis can move under the
force of gravity. To overcome this problem, use a servo motor with a
brake.
While the spindle motor is running, shutting off the motor–driving power
to the spindle amplifier allows the spindle motor to continue running
under its own inertia, which is quite dangerous. When the emergency stop
signal (*ESP) contact opens, it is necessary to confirm that the spindle
motor has been decelerated to a stop, before the spindle motor power is
shut off.
The FANUC control amplifier α series products are designed to satisfy
the above requirements. The emergency stop signal should be input to the
power supply module (called the PSM). The PSM outputs a motor power
MCC control signal, which can be used to switch the power applied to the
power supply module on and off.
The CNC controller is designed to detect overtravel by using a software
limit function. Normally, no hardware limit switch is required to detect
overtravel. If the machine goes beyond a software limit because of a servo
feedback failure, however, it is necessary to provide a stroke end limit
switch, connected so that the emergency stop signal can be used to stop
the machine.
Fig. 10 shows an example showing how to use the emergency stop signal
with this CNC controller and α series control amplifier.
WARNING